The present invention relates to hydraulic control systems and pertains particularly to means for equalizing temperature within a hydraulic system.
Many hydraulic systems employ individual hydraulic circuits having separate pumps and motors drawing fluid from a common reservoir. Said systems are frequently employed in machines or on vehicles wherein one of the motors may operate substantially continuously and one or more of the motors may operate very infrequently. A motor that operates continuously generates a considerable amount of heat which is transferred to the fluid of the system. On the other hand, motors which operate very infrequently may have a temperature which is considerably below that of the motors which operate rather continuously. When fluid from a common reservoir is directed to a motor which is considerably cooler than the temperature of the fluid, the motor becomes subject to thermal shock by the hot fluid directed thereto. This is an especially severe problem in cold climates and during cold weather.
The heat from such hot fluid can cause distortion in the mechanical components of the motor which may result in the motor binding or components of the system cracking.
An example of such systems which employ separate circuits drawing fluid from the same reservoir is illustrated in U.S. Pat. No. 3,815,478 wherein the hydraulic system is utilized to operate the draw works of a pipelayer. In such a system the winch for manipulating the boom is normally operated by a rotary hydralic motor which is very infrequently used because the boom may stay in the same position for a considerable period of time. On the other hand, the winch motor which operates a winch for lifting loads suspended from the boom may be operated substantially continuously. Thus, the infrequently used motor may have a temperature which is considerably below that of the operating fluid. This is especially a problem in cold climates such as the Alaskan oil fields wherein pipelayer machines are extensively used to lay pipelines for transporting crude oil from the oil fields.